Method of forming shallow trench isolation with rounded corner and divot-free by using disposable spacer

A method of fabricating an STI, comprising the steps of:

• providing a silicon structure having a pad oxide layer formed thereover;
• forming an undoped poly buffer layer over the pad oxide layer;
• forming a top oxide hard mask layer over the undoped poly buffer layer;
• patterning the top oxide hard mask layer, the undoped poly buffer layer and the pad oxide layer to form an opening exposing a portion of the silicon structure within an active area;
• the opening having exposed side walls;
• forming nitride spacers over the exposed side walls;
• using the patterned top oxide hard mask layer and the nitride spacers as hard masks, etching the silicon structure to form an STI opening within the active area;
• removing the nitride spacers exposing the upper corners of the STI opening;
• using an oxidation process, forming a liner oxide layer within the STI opening, over the upper corners of the STI opening and at least the patterned undoped poly buffer layer exposed by the removal of the nitride spacers;
• forming an STI oxide layer over the patterned hard mask layer filling the liner oxide layer lined STI opening;
• and
• removing the patterned top oxide hard mask and planarizing the STI oxide layer by a planarization process;
• removing the patterned undoped poly buffer layer;
• and
• removing the patterned pad oxide layer to fabricate the STI having rounded corners and without substantial divots.

A method of fabricating an STI, comprising the steps of:

• providing a silicon structure having a pad oxide layer formed thereover;
• forming an undoped poly buffer layer over the pad oxide layer;
• forming a nitride hard mask layer over the undoped poly buffer layer;
• patterning the nitride hard mask layer, the undoped poly buffer layer and the pad oxide layer to form an opening exposing a portion of the silicon structure within an active area;
• the opening having exposed side walls;
• forming oxide spacers over the exposed side walls;
• using the patterned nitride hard mask layer and the oxide spacers as hard masks, etching the silicon structure to form an STI opening within the active area;
• removing the oxide spacers exposing the upper corners of the STI opening;
• using an oxidation process, forming a liner oxide layer within the STI opening, over the upper corners of the STI opening and at least the patterned undoped poly buffer layer exposed by the removal of the oxide spacers;
• forming an STI oxide layer over the patterned nitride hard mask layer filling the liner oxide layer lined STI opening;
• and
• planarizing the STI oxide layer down to the patterned nitride hard mask;
• removing the patterned nitride hard mask and the patterned undoped poly buffer layer;
• and
• removing the patterned pad oxide layer to fabricate the STI having rounded corners and without substantial divots.